The present invention relates to a bi-directional optical transmission and reception system for executing transmission and reception by using one-core optical fiber. The present invention also relates to an optical transmission and reception module and an optical cable for use in the optical transmission and reception system. In particular, the present invention relates a digital communication system such as IEEE 1394 and USB2 capable of making high-speed transmission.
A plastic optical fiber cable has been hitherto used in optical communication at home. The plastic optical fiber cable is flexible, can be wired easily, and costs low. Therefore, audio digital signals are actually transmitted in domestic networks, such as audiovisual devices and personal computers, through the plastic optical fiber cable.
At home, it is expected that various factors such as rearrangement of furniture in a room cause frequent alteration of wiring of the optical fiber cable, accompanied with the removal and installation of an optical plug and/or elongation of the optical fiber cable. It is also expected that a user switches a communication medium, depending on use conditions. That is, in a short-distance low-speed communication, optical spatial transmission will be used, whereas in long-distance high-speed communication, the optical fiber cable will be used. To meet the need, development of optical transmission and reception systems are being made.
The protocols (communication methods) in the optical transmission and reception system are classified into a full duplex communication method and a half duplex communication method. The former is capable of accomplishing transmission and reception simultaneously, whereas the latter is incapable of accomplishing reception unless transmission has terminated. It is conceivable that real time transmission of information will be mainly made even at home in the near future. Thus, the construction of the optical transmission and reception system adopting the full duplex communication method is desired.
As an example of a conventional optical transmission and reception module for realizing such an optical transmission and reception system, an optical transmission and reception module proposed in the Japanese Patent Application Laid-Open No. 7-248429 is described below with reference to FIG. 1. The optical transmission and reception module is intended to be compact and inexpensive by adopting the Foucault prism as an optical branching element.
According to the proposed optical transmission and reception module, transmission light T emitted by a light emitting element 101 transmits through a cover glass 102 installed on a package and is divided into halves by a Foucault prism 103. After condensed by a condenser lens 104, a half is coupled to, or incident on, an optical fiber 107 through a rod lens 105. On the other hand, reception light rays R discharged from an optical fiber 107 having the rod lens 105 disposed at its front end are condensed by the condenser lens 104, incident on the Foucault prism 103, and then divided into halves. After they pass through the cover glass 102, only a half is coupled to a light receiving element 106.
However, the disposition relationship between the light emitting element 101 and the light receiving element 106 shown in FIG. 1 forces the light receiving element 106 to be located at a position apart from the condensed point of the reception light R. Accordingly, to detect the diverged reception light R, it is necessary to prepare a large light receiving element 106. Consequently, the electrostatic capacity of the light receiving element 106 is large. Thus it is difficult to realize a high-speed communication.
The limitative position of the light receiving element 106 may be caused by that the light-condensing system consists of the single condenser lens 104 interposed between the optical fiber 107 and the Foucault prism 103 and that the vertical angle of the Foucault prism is as small as 2-3 degrees, as described in a paragraph denoted by [0018] of the Japanese Patent Application Laid-Open No. 7-248429.
As another prior art example, there is an optical transmission and reception module proposed in the Japanese Patent Application Laid-Open No. 10-39181, which module carries out optical transmission and reception through one optical fiber by the half duplex communication method, as shown in FIG. 2.
According to the optical transmission and reception module, half of transmission light rays T emitted by a laser diode LD serving as a light emitting element are reflected from a 50%-beam splitter film BS formed on a prism 121 provided on a light receiving element PD, condensed by a lens 122, and connected to an optical fiber 123. On the other hand, half of reception light rays R discharged from the optical fiber 123 pass through the beam splitter film BS and are connected to the light receiving element PD.
This prior art is advantageous in that one optical fiber is used to carry out the optical transmission and reception by the half duplex communication method. However, because light is branched by means of the beam splitter film BS formed on the prism 121, the optical amount is reduced to half in each of the transmission and the reception. Thus, the optical transmission and reception module is not suitable for a long-distance transmission and reception of an optical signal.
As still another prior art example, there is an optical transmission and reception module proposed in the literature xe2x80x9cMiniaturized Transceiver using Simplex POF for IEEE 1394 (International POF Conference ""99, pages 205-208)xe2x80x9d. The optical transmission and reception module carries out optical transmission and reception through one optical fiber by the full duplex communication method, as shown in FIG. 3.
According to the optical transmission and reception module, transmission light rays T are emitted by an LD serving as the light emitting element, condensed by a cylindrical lens 131, reflected from a reflection film 133 (99%) formed on a prism 132, and converged. The converged light is connected to, or incident on, an end surface of the optical fiber. On the other hand, reception light rays R are discharged from the optical fiber and are mostly connected to a photodiode PD, although a part of the light rays R is lost by the reflection film 133. According to the method, because the light rays are connected to the optical fiber, with the light rays converged, in principle, Fresnel light on the end surface of the optical fiber is not connected to the photodiode PD. Thus, the full duplex transmission and reception can be accomplished with one optical fiber.
The prior art shown in FIG. 3 has merits because it can accomplish transmission and reception by using one optical fiber, has only a small light loss in a transmission time, and the transmission light T and the reception light R can be almost completely separated from each other, i.e., the full duplex optical system can be realized. However, in the prior art, the reflection film 133 is formed on the prism, and the cylindrical lens 131 is formed on the reflection film 133. That is, a large number of processes are required in the stage of preparing the optical branching elements. Consequently, the manufacturing cost is high. Further, because the reception light rays R do not pass through a lens, the light receiving element PD is required to be large. Consequently, the electrostatic capacity of the light receiving element PD is large. That is, the conventional art is unsuitable for high-speed communication.
Sharp Kabushiki Kaisha has proposed an optical transmission and reception system as shown in FIGS. 4A and 4B in the Japanese Patent Application No. 11-5872 (filed on Jan. 12, 1999).
In the optical transmission and reception system, it is possible to use a digital audio optical fiber cable which has already spread, and execute two-way communication through one optical cable having one-core optical fiber.
The optical transmission and reception system has an optical cable 41 and an optical transmission and reception module 51.
The optical cable 41 has in its inside a one-core optical fiber 42 serving as the optical path, and has a plug 43 at both ends thereof. The plug 43 is connected to the optical transmission and reception module 51.
The holding member 52, of the optical transmission and reception module 51, having an insertion hole 52a houses a light emitting element 53 converting an electrical signal into an optical signal, a light receiving element 54 converting an optical signal into an electrical signal, a mold package 55 sealing the light emitting element 53 and the light receiving element 54, lenses 55a, 55b formed integrally with the mold package 55, and an optical branching element 56.
The optical cable 41 and the optical transmission and reception module 51 are optically connected to each other by inserting the plug 43 of the optical cable 41 into the insertion hole 52a of the optical transmission and reception module 51.
More specifically, transmission light rays emitted by the light emitting element 53 transmit through the lens 55a formed integrally with the mold package 55, so as to be collimated with one another. Then, the collimated light rays are deflected to the optical-axis direction of the optical fiber 42 by a microprism formed on the surface of the optical branching element 56, and are incident on the optical fiber 42.
On the other hand, light rays discharged from the optical fiber 42 are deflected by the microprism formed on the surface of the optical branching element 56, transmit through the lens 55b formed integrally with the mold package 55, and incident on the light receiving element 54 as condensed light rays.
However, the optical transmission and reception module and the light transmission and reception system using it have the following problems, which will be described below with reference to FIG. 5.
1) Because the light emitting element 53 and the light receiving element 54 are sealed in the single mold package 55, the light rays emitted by the light emitting element 53 travels along a path L1 in the mold package 55 to be incident on the light receiving element 54. As a result, high crosstalk is generated, and this makes impossible to carry out the full duplex communication method.
2) Because the light rays emitted by the light emitting element 53 and the light rays to be received by the light receiving element 54 are deflected by the same optical branching element 56 within the module, the light rays emitted by the light emitting element 53 are reflected from the optical branching element 56 and are incident on the light receiving element 54 along a path L2. As a result, high crosstalk is generated and thus it becomes impossible to carry out the full duplex communication method.
3) Because the same optical fiber 42 is used as both the transmission line for the optical signal from the light emitting element 53 and the transmission line for the optical signal to the light receiving element 54, the signal light rays emitted by the light emitting element 53 are reflected from both end surfaces of the optical fiber 42 and are incident on the light receiving element 54 along a path L3. Thus, high crosstalk is generated, which makes impossible to carry out the full duplex communication method.
4) The optical transmission and reception module is optically connected to its counterpart via the optical fiber 42. Thus, supposing that the optical transmission and reception module and its counterpart (on the left-hand side of the figure) have the same construction, the light rays emitted by the light emitting element 53 will be reflected by an optical branching element 56 of the counterpart and then incident on the light receiving element along a path L4. As a result, high crosstalk will be generated and thus it will be impossible to carry out the full duplex communication method.
As a prior art light-branching device, there is one disclosed in Japanese Utility Model Application Laid-Open No. 64-45805.
FIG. 6 is a schematic partial sectional view of the light-branching device. FIG. 7 shows an end face on the side of a transmission-line optical fiber of a central portion of the light-branching device of FIG. 6.
As shown in FIGS. 6 and 7, in the light-branching device, a pair of bare optical fibers 161, 161 are combined with each other with a reflection film 162 of a predetermined length disposed therebetween. The end surfaces of the bare optical fibers 161, 161 combined with each other are coaxially disposed in opposition to the end surface of a transmission-line optical fiber 163.
In the case where the light-branching device is used as the light-branching element for an optical transmission and reception module, a problem occurs. The problem is described below with reference to FIGS. 6 and 7.
1) Each time the optical fiber 163 is connected to the light-branching device and disconnected therefrom, the transmission-line optical fiber 163 contacts the bare optical fibers 161, 161 of the light-branching device at their end surfaces confronting the optical fiber 163. Consequently, the mutually confronting end surfaces of the bare optical fibers 161, 161 and transmission-line optical fiber 163 will be damaged. Thus, the transmittances thereof deteriorate.
2) Reflected light is generated on the end surface of the reflection film 162 which contacts the end surface of the optical fiber 163. The reflected light, which is an optical transmission signal emitted by a light emitting element of a counterpart of the pertinent module, will be incident on a light receiving element of the counterpart. In the case where the counterpart has the same construction as that of the pertinent optical transmission and reception module, reflected light is generated also on the end surface of a reflection film of the counterpart, and the reflected light of transmission light emitted by the light emitting element of the pertinent optical transmission and reception module will be incident on the light receiving element of the same. Consequently, crosstalk will be high and it will be impossible to carry out the full duplex communication method.
In view of the problems, it is an object of the present invention to provide an optical transmission and reception system suppressing crosstalk and allowing optical transmission and reception to be accomplished by a full duplex communication method, as well as providing an optical transmission and reception module and an optical plug for the optical transmission and reception system.
There is provided, according to an aspect of the invention, an optical transmission and reception module for duplex-communication performing optical transmission and reception through an identical optical fiber, comprising:
a light emitting element for emitting transmission light;
a light receiving element for receiving reception light;
a transmission optical system disposed in a position that falls between the light emitting element and an end surface of the optical fiber when the optical fiber is in place in the module;
a reception optical system disposed in a position that falls between the light receiving element and the end surface of the optical fiber when the optical fiber is in place in the module; and
a Foucault prism having:
a first inclined surface for refracting the transmission light coming from the light emitting element and taken out by the transmission optical system, and coupling the refracted transmission light to the end surface of the optical fiber; and
a second inclined surface for refracting at least part of the reception light discharged from the optical fiber, and coupling the refracted reception light to the light receiving element through the reception optical system.
With the above arrangement, the transmission light taken out from the light emitting element through the optical system is refracted only by the first inclined surface of the Foucault prism. Thus, in principle, loss of light does not occur on the Foucault prism and thus the transmission light can be efficiently connected or coupled to the optical fiber. Further, most of return light rays including principle light rays generated by Fresnel reflection in connecting the transmission light to the optical fiber return to the first inclined surface of the Foucault prism. Therefore, it is possible to reduce the amount of the transmission light that enters the light receiving element of the module at the transmission end. Accordingly, a highly efficient optical communication can be realized in the optical transmission and reception module to be used for the full duplex communication schemes that carry out optical transmission and reception simultaneously. Further, using the Foucault prism having the above configuration as a branching element can reduce the size of the optical transmission and reception module in the longitudinal direction.
At least one of the light emitting element and the light receiving element may be sealed with a resin, and the resin may form a lens of the transmission optical system or the reception optical system on a straight line connecting a light emitting surface or a light receiving surface to the corresponding inclined surface of the Foucault prism.
For example, the light emitting element and/or the light receiving element can be resin-molded, and in the resin-molding process a lens can be integrally formed so as to be directed toward the corresponding inclined surface (first and/or second inclined surface) of the Foucault prism. By thus doing, transmission efficiency and/or reception efficiency can be improved. Further, if the periphery of the light emitting element is sealed with the resin, the critical angle at a resin-air interface is increased. Thus, the light take-out efficiency can also be improved.
The light emitting element and the light receiving element may be mounted on an identical substrate which is disposed, for example, on a plane almost parallel to the Foucault prism. By thus doing, the mounting process steps for the individual elements can be facilitated. Therefore, it is possible to reduce the number of manufacturing process steps and shorten working period of time, and further facilitate the positioning of the substrate relative to the optical transmission and reception module. Eventually, the mass-production price can be reduced.
Both the light emitting element and the light receiving element may be sealed with a resin, and the resin may form lenses of each of the transmission optical system and the reception optical system on straight lines connecting each of a light emitting surface and a light receiving surface to the first and second inclined surfaces of the Foucault prism, respectively.
For example, the light emitting element and the light receiving element can be resin-molded, and in the resin-molding process lenses can be integrally formed so as to be directed toward their respective associated inclined surfaces of the Foucault prism. By thus doing, both the transmission efficiency and the reception efficiency can be improved. Further, because the periphery of the light emitting element is sealed with the resin, the critical angle at a resin-air interface is increased. Thus, light take-out efficiency is also improved.
A condenser lens for use in both transmission and reception operations is provided between the Foucault prism and the light emitting and receiving elements. In this case, in a transmission time, the transmission optical system such as a lens is not required to converge light rays coming from the light emitting element. That is, the condenser lens converts light rays, even diffused light rays, coming from the transmission optical system into converged light rays. This arrangement provides against the dislocation of the optical fiber relative to a transmission part of the module. On the other hand, in a reception time, light rays discharged from an end of the optical fiber diffuse or spread at an angle determined by the NA value (numerical aperture) of the optical fiber. Thus, the light rays refracted by the Foucault prism will also diffuse. However, before they diffuse, they are collimated with one another by the condenser lens. Then, they are coupled to the light receiving element with the aide of the reception optical system such as a lens. Accordingly, it is possible to greatly improve efficiency in the reception time.
The Foucault prism and the condenser lens may be formed integrally by, for example, injection molding. By thus doing, it is possible to reduce the number of component parts and thus reduce the number of manufacturing process steps and shorten a working time period, which makes it possible to reduce the cost for manufacturing the optical transmission and reception module. It is also possible to suppress Fresnel reflected light which would be generated in the interface between the condenser lens and the Foucault prism if they are provided separately.
If a partitioning member is interposed between a transmission part and a reception part of the module, it is possible to prevent the transmission light from being directly connected as turbulent light to the light receiving element. Thereby, the S/N ratio at the light receiving element can be improved. Accordingly, a high-quality full duplex communication system can be realized.
The partitioning member may, preferably, be movable in a principal axis direction of the optical fiber when the partitioning member comes into contact with or strikes against an end surface of the optical fiber. This arrangement can be achieved by, for example, by providing the partitioning member, such as a partitioning plate, with a jig such as a spring that allows the partitioning plate to move to the depth of the module when the end surface of the optical fiber comes into contact with the partitioning plate. The movable partitioning plate enables to prevent the end surface of the optical fiber from being damaged by the contact with the partitioning plate. Thus, efficiency in optical transmission and reception is prevented from deteriorating due to the damage of the optical fiber end surface.
The partitioning member may, preferably, have an optical reflecting property. For example, by using a light-tight plate, or light-screening plate, as the partitioning member, having a sufficiently high reflectance or reflectivity of 80% or higher for the transmission light and the reception light, it is possible to effectively utilize as the reception light even such light as would be absorbed in a light reception time if the partitioning member has a surface having a high absorptivity.
Preferably, an end surface of the partitioning member confronting the end surface of the optical fiber may have an optical absorbing property. For example, a light-tight plate whose end surface has a sufficiently high absorptivity of 80% or higher for the transmission light and the reception light can be used as the partitioning member. Then, it is possible to reduce a so-called a xe2x80x9cfar-side reflectionxe2x80x9d, namely the reflection of the transmission signal at the side of a counterpart module currently serving as the reception end (in this case the reflection is caused by an end surface of the partitioning member in the counterpart module). Thus, the S/N ratio at the light receiving element can be improved.
A curvature of the lens, formed of the sealing resin, of the transmission optical system may be so set that a bundle of convergent light rays falling within a numerical aperture is incident on the end surface of the optical fiber. Alternatively or additionally, a curvature of the condenser lens may be so set that a bundle of convergent light rays falling within a numerical aperture is incident on the end surface of the optical fiber.
By thus making the transmission light incident on the end surface of the optical fiber at an angle such that the transmission light becomes convergent light of a size corresponding to the NA value of the optical fiber or smaller, it is possible to prevent Fresnel reflected light off the near-side end surface of the optical fiber from disadvantageously entering the light receiving element in the module serving now as the transmission end. Thus, the S/N ratio at the light receiving element can be improved. In other words, the utilization efficiency of the transmission light emitted by the light emitting element can be improved to a higher extent.
There is also provided, according to another aspect of the invention, An optical transmission and reception module, comprising a light emitting element emitting transmission light and a light receiving element receiving reception light, for transmitting and receiving the light by using an identical one-core optical fiber, further comprising:
a light-tight partitioning plate touching an end surface of the optical fiber when the optical fiber is in place in the module, and separating an optical path of the transmission light and that of the reception light from each other.
With this arrangement, it is possible to prevent the transmission light emitted by the light emitting element from being reflected by the near-side end surface of the optical fiber (namely, the end surface near this module of the optical fiber) to eventually enter the light receiving element of the same module. Thus, it is possible to suppress crosstalk caused by the influence of the reflection of the transmission light by the near-side end surface of the optical fiber. As a result, optical transmission can be accomplished by the full duplex communication method.
In one embodiment, the partitioning plate is located at a position where the partitioning plate is pressed by the end surface of the optical fiber when the optical fiber is fitted into the module, and the partitioning plate is elastically deformable when pressed by the end surface of the optical fiber.
With this arrangement, even though there are variations in installed length of optical fibers because of molding variations, it is possible to absorb the variations by the mounted position and the elastic deformation of the partitioning plate. Thus, the partitioning plate does not fail to be in contact with the near-side end surface of the optical fiber. Accordingly, irrespective of the variations in installed length of optical fibers, crosstalk caused by the influence of the reflection of the transmission light by the near-side end surface of the optical fiber can be suppressed, so that optical transmission can be accomplished by the full duplex communication method.
The partitioning plate may have a partitioning portion touching the end surface of the optical fiber and an elastically deformable portion that elastically deforms when the partitioning plate is pressed by the end surface of the optical fiber.
With this arrangement, even though the end surface of the optical fiber presses the partitioning portion, the partitioning portion is prevented from being slid laterally on the optical fiber end surface or deformed into an arcuate shape. Further, it is possible to prevent the partitioning plate from rubbing against the end surface of the optical fiber or striking a corner of the partitioning plate against the end surface of the optical fiber. Thus, the end surface of the optical fiber is prevented from being damaged.
In one embodiment, a light absorbing layer is formed on a contact surface of the partitioning plate that touches the end surface of the optical fiber.
With the construction, it is possible to prevent transmission light coming from an associated module, which is connected with the pertinent module through the optical fiber, from being reflected by the contact surface of the partitioning plate and entering the light receiving element of the associated module. Consequently, it is possible to suppress crosstalk at the associated module caused by the influence of light reflected from the contact surface of the partitioning plate.
The partitioning plate may be extended toward the light emitting and receiving elements such that the partitioning plate is interposed between optical elements provided between the end surface of the optical fiber and each of the light emitting and receiving elements, and/or interposed between the light receiving element and the light emitting element.
According to the construction, it is possible to prevent the transmission light emitted by the light emitting element and reflected from the rear surfaces of the optical elements in the module from entering the light receiving element of the same module. Alternatively or additionally, it is possible to cut off the transmission light propagating toward the light receiving element in the same module through, for example, a mold package sealing the light emitting and receiving elements. Thus, such transmission light does not enter the receiving element in the same module. That is, it is possible to suppress crosstalk caused by the influence of the light reflected by the rear surfaces of the optical elements or the light propagating in the mold package in the module.
In one embodiment, the partitioning plate may be formed of an electrically conductive material and an electrical potential of the partitioning plate is set to a ground potential.
With the construction, it is possible to prevent an inductive coupling between the light emitting element and the light receiving element in the same module and thus suppress crosstalk caused by the influence of the inductive coupling in this module.
In one embodiment, optical elements are disposed between the end surface of the optical fiber and each of the light emitting and receiving elements, and an anti-reflection film is formed on an optical-fiber-side surface of each optical element
With the construction, it is possible to prevent the transmission light emitted by a light emitting element in an associated module from being reflected by the surfaces of the optical elements to disadvantageously enter a light receiving element of the associated module. That is, it is possible to suppress crosstalk in the associated module caused by the influence of the light reflected by the surfaces of the optical elements.
Each optical element disposed between the light emitting and receiving elements and the near-side end surface of the optical fiber may comprise an optical deflection element, and the light receiving element and the light emitting element may be inclined relative to optical axes of the optical deflection elements.
This arrangement prevents the transmission light emitted by a light emitting element of an associated module, or a counterpart of the present module, from being reflected by the light emitting element and the light receiving element of the present module to enter a light receiving element of the associated module.
According to another aspect of the invention, there is also provide comprising:
The optical transmission and reception module as described above combined with an optical cable having a one-core optical fiber inside constitutes an optical transmission and reception system. In this system, the optical fiber has inclined end surfaces.
In this system, it is possible to prevent the transmission light sent from one end surface of the optical fiber from being reflected from the other end surface thereof to enter a light receiving element of a module in which the other end surface of the optical fiber is received. Consequently, it is possible to suppress crosstalk caused by the influence of light reflected by the far-side end surface of the optical fiber (namely, the end surface at the side far from the relevant module). Thus, optical transmission can be accomplished by the full duplex communication method.
In the aforementioned optical transmission and reception system in which the partitioning plate is in contact the end surface of the optical fiber, when the optical plug is rotated, with the end surface of the optical fiber in contact with the partitioning plate, there is a possibility that the end surface of the optical fiber and/or the partitioning plate is broken. To avoid this, it is necessary to provide the optical plug and the optical transmission and reception module with an anti-rotation mechanism. The anti-rotation mechanism can be realized by, for example, providing the optical plug with a key while providing the optical transmission and reception module with a keyway. However, unless the anti-rotation key is fitted in the keyway of the optical transmission and reception module, the optical plug cannot be inserted into the optical transmission and reception module. This is an inconvenience to the user.
Accordingly, it is another object of the present invention to provide an optical transmission and reception module which uses a light-tight partitioning plate to enable an optical transmission according to the full-duplex communication method, as well as providing an optical cable and an optical transmission and reception system using the module and the optical fiber, in which rotation of an optical plug in the optical transmission and reception module causes damages to neither the end surface of the optical fiber nor the partitioning plate.
To achieve this object, there is provided, according to a further aspect of the invention, an optical transmission and reception module, comprising a light emitting element emitting transmission light and a light receiving element receiving reception light, for transmitting and receiving the light by using an identical one-core optical fiber, further comprising:
a light-tight partitioning member separating an optical path of the transmission light and that of the reception light from each other,
wherein the partitioning member has an opposed surface to be opposed to an end surface of the optical fiber, with a gap left between the partitioning member and an end surface of the optical fiber, when the optical fiber is in place in the module.
With the above construction, when the optical plug accommodating the optical fiber is mounted inside the optical transmission and reception module, there is a gap between the end surface of the optical fiber and the opposed surface of the partitioning member confronting the end surface of the optical fiber. Thus, these mutually confronting surfaces do not contact each other even when the optical plug rotates. Thus, it is possible to prevent these members from being damaged. Therefore, it is unnecessary to provide the optical transmission and reception module and the optical plug with any anti-rotation mechanism. Thus, the user can fit the optical plug in the optical transmission and reception module easily.
From the viewpoint of the optical transmission by the full duplex communication method, the gap (G) may be, preferably, in the range of 0 mm less than G less than 0.3 mm, and more preferably about 0.2 mm. When the gap lies in this range, the bit error rate (BER) can be reduced to 1E-12 (i.e., 10xe2x88x9212), although depending somewhat on the optical system, and hence it is possible to achieve optical transmission by the full duplex communication method.
The partitioning member may have a positioning means for, when the optical fiber is placed in position in the module, positioning the opposed surface relative to the end surface of the optical fiber such that the gap is constant. By providing the partitioning member with the positioning means, the dimension of the gap between the end surface of the optical fiber and the opposed surface of the partitioning member is prevented from changing each time the optical plug is inserted in the optical transmission and reception module. Accordingly, it is possible to carry out full duplex communication stably.
In one embodiment, the positioning means comprises an engaging surface to touch an end surface of an optical plug holding the optical fiber therein, and the engaging surface has a fixed positional relationship with the opposed surface.
In another embodiment, the positioning means comprises an engaging surface to touch a portion of the end surface of the optical fiber through which portion light does not pass, and the engaging surface has a fixed positional relationship with the opposed surface.
It is preferable to use a slippery material, namely, a material having a low coefficient of sliding friction for the engaging surface. Even though the optical plug is rotated a lot of times, the contact portion is hardly broken.
The partitioning member may have a spring means urging the engaging surface toward the optical fiber. In this case, the engaging surface is pressed against the end surface of the optical plug or a portion of the end surface of the optical fiber through which light does not pass. Thus, it is possible to prevent the dimension of the gap from being varied while the optical plug is in the module.
In one embodiment, the partitioning member comprises:
a partitioning plate disposed between the light emitting element and the light receiving element and having the opposed surface;
an engaging portion to which the partitioning plate is fixed and which has the engaging surface; and
a holding portion holding the engaging portion such that the engaging portion is movable in a direction of an optical axis of the optical fiber, the holding portion having a spring means for urging the engaging portion to the optical fiber.
With this arrangement, when a comparatively long optical plug is inserted in the module, the engaging portion moves toward the bottom of the module (to the side opposite to a plug insertion hole) from an initial position against the spring force of the spring means, while the engaging portion is being held by the holding portion. As a result, the engaging surface moves toward the bottom of the module from the initial position. Accordingly, by setting a position corresponding to a conceivable shortest length of the optical plug as an initial position of the engaging portion in consideration of variations (tolerance) of the length of optical plugs in a manufacturing stage, the movement of the engaging portion absorbs the variations.
In one embodiment, the engaging portion has a generally truncated-cone-shaped hole and receives a front end of the optical plug having an optical fiber in the hole.
When the opposed surface of the partitioning member is complementary in shape to the end surface of the optical fiber, the dimension of the gap can be reliably allowed to be constant over the entire end surface of the optical fiber.
Furthermore, the present invention provides an optical cable having a one-core optical fiber passed therethrough, wherein each of end surfaces of the optical fiber is a curved surface rotationally symmetrical about an optical axis of the optical fiber. Use of such an optical cable prevents transmission light sent from one end surface of the optical fiber from being reflected by the other end surface thereof to be back to the one end surface and eventually enter the light receiving element.
The rotationally symmetrical curved surface is, for example, a convex surface. Alternatively, it may be a cone-shaped surface.
A combination of any of the optical transmission and reception modules and the optical cable can provide an optical transmission and reception system which are not subject to damages of the optical fiber and the partitioning member due to the rotation of the optical plug in the module, which reliably accomplishes the full duplex optical communication, and which provides a convenience to a user.
Each end surface of the optical fiber may project from a plug provided at opposite ends of the optical fiber, and a radially outward portion of the end surface of the optical fiber may cover a part of an end surface of the plug. The structure of the end surfaces of the optical fiber may be adopted especially in the embodiment in which the engaging surface of the partitioning member touches a portion of the end surface of the optical fiber through which light does not pass.
Other objects, features and advantages of the present invention will be obvious from the following description.